Many ophthalmological devices nowadays have approaches for largely automatic alignment of the visual axis of the eye with the optical axis of the ophthalmological device. For the automatic alignment, numerous approaches are known from the prior art in which the two axes are usually adjusted with respect to one another automatically.
For example, DE 102 50 569 A1 describes an approach for positioning a device in x, y, and/or z coordinates with respect to an eye of a patient to be examined. In the ophthalmological device, the eye tracker unit, which has at least two different, adjustable magnifications is used for this purpose. The signal of the eye tracker unit is used not only for tracking a measuring mark and/or grid structure projected onto the eye, but also for detecting the position of the eye of the patient with respect to the optical axis of the ophthalmological device. Based on the determined position of the eye of the patient, appropriate control signals for positioning drives are then generated.
Another approach for positioning an ophthalmological device with respect to an eye of a patient to be examined is described in DE 102 50 570 A1. In this approach, however, the signals of an image recording unit, which for this purpose has an additional wide-angle setting, are used for the positioning. Here as well, a setpoint value concerning the magnitude and direction for the positioning device is generated and supplied to a positioning unit.
U.S. Pat. No. 7,401,921 B2 describes an automatic, motor-driven patient positioning aid for an ophthalmological measuring device. The motorized patient head support is likewise composed of a chin rest and a forehead support, of which there are two of each for orientation to the right or the left eye, and a corresponding motor assembly to allow movement of the head in three directions (X, Y, Z).
However, all three approaches require that for this automatic alignment process, the eye of the patient must have been brought into a fixed position using the chin rest and forehead support that are present; i.e., a rough adjustment of the ophthalmological device to the particular patient must have been made beforehand.
Since the range of motion of ophthalmological devices is restricted to approximately 30 mm on account of the limited height between the surface of the work table and the eye of the patient, the head of the patient is usually roughly positioned in advance, using the height adjustment of the chin rest. In addition, the distance from the chin rest to the forehead support must be correctly adjusted to the head size of the patient in order to achieve sufficient stability of the head.
The height adjustment of ±15 mm of the device is usually adequate to allow treatment of the vast majority of patients. However, for patients having head sizes in the borderline range, or also for children, additional corrections of the chin rest and of its distance from the forehead support are necessary. This cannot be omitted, since otherwise the eye may not be detectable under some circumstances, and an examination and/or treatment may not be possible. This is possible only after a subsequent correction, which results in disruption of the accustomed process, and thus, time delays and unnecessary waiting times.
However, assuming that the vertical distance between the bottom edge of the chin and the eye (canthus height) varies between 80 and 140 mm in patients, this results in a tolerance range of 60 mm. The tolerance range of 60 mm is much too large for fine positioning of ophthalmological devices in which the head of the patient is already resting on the chin support. Thus, there is a need for rough adjustment of the ophthalmological device to the particular patient, in particular, prior to fine positioning of the device.
As soon as an alignment of a patient with respect to a device via automatic movement is to be carried out, the question arises as to how possible collisions between the device and the patient may be avoided.
According to the prior art, in contrast to the above-described approaches concerning the fine adjustment of a ophthalmological device, rough positioning of the ophthalmological device to individual patients is not known. Instead, the rough alignment heretofore has generally been carried out manually, based on known patient data or by visual adjustment by the operator.
In this regard, U.S. Pat. No. 4,139,280 A describes a manual positioning aid for the positioning of patients with respect to the optical axis of an ophthalmological examination system, which is moved by purely mechanical means and which ensures maximum freedom of movement for the ophthalmologist. It is disadvantageous here that the operator must manually position the height of the eye of the patient.
The approach described in DE 198 16 486 A1 relates to a universal, modular examination system for examining human vision. To comfortably fix the head in a normal upright, relaxed posture, a modified head support composed of a chin rest and a forehead rest is used in combination with a functionally adapted seating device. The height-adjustable chair as well as the head support are mechanically adapted to the patient, so that the head of the patient cannot be turned during the examination and is kept still. Only in this way is it possible to ensure error-free examination results.
U.S. Pat. No. 6,309,068 B1 describes an automatic adjustment of a patient positioning aid, in which the ophthalmological system assesses whether the eye is already in the field of vision of the recording unit of the ophthalmological system when the head of the patient is present in the head support. By use of a control unit, the height of the chin rest is automatically adapted by application of a spring drive and a stopper lock. However, anatomically correct dimensions of facial features, which are necessary for correct positioning and the definition of safety distances and safety zones, are not detected.
However, the approaches known from the prior art have the disadvantage either that they are not suitable for the fine adjustment between the visual axis and the optical axis of the ophthalmological device, or that the rough positioning of the ophthalmological device to the eye of the patient is carried out manually, based on known patient data or by visual adjustment by the operator.
The known automated approach discloses no anatomically correct determination of facial dimensions, which are necessary for the rough positioning and definition of safety distances and safety zones.